The present application is based on and claims the priority of German Patent Application 196 40 042.2, that was filed on Sep. 30, 1996. The entire disclosure of the German Priority Application 196 40 042.2 is incorporated herein by reference.
The invention relates to a method and apparatus for forming crosswise score lines which facilitate later folding along such score lines, on pre-cut sheet goods blanks, and especially pre-cut envelope blanks, using at least one scoring roller and one counter roller.
It is generally known to form one or more score lines on a pre-cut sheet goods blank, in order to facilitate the subsequent folding of the blank along these score lines. Such a score line does not involve the folding or pleating of the blank, but rather merely weakens the material of the blank along this score line so that the blank can be subsequently folded, easily, sharply and precisely along the provided score line. To this end, the score line may involve a compression or reduction of the thickness of the blank material along the score line, or may involve a rupturing or weakening of at least some of the fibers of the blank material along the score line, or may involve a perforation of the blank material along the score line.
The formation of one or more crosswise score lines on an envelope blank or on a blank for a shipping bag or the like is generally subject to particular problems and difficulties if the material of the blank is non-elastic to a great extent, for the following reasons. Typically, in order to form a score line, a scoring knife or blade is used to push the material of the blank into a groove or recess provided in a counter tool such as a counter roller. If the material of the blank, such as paper for example, is not sufficiently elastic, then the scoring knife or blade will try to push the paper material into the groove or recess of the counter tool, but the paper is not well suited to allow this to occur. Namely, the non-elastic paper will be either stretched or torn during the scoring operation, or, if the paper does not yield, then the position and alignment of the pre-cut blank will be shifted or offset relative to the cycling of the machine. For this reason, the normally rigid and non-elastic blank is typically held and guided in specific, complicated ways using specific complicated means, which becomes evident in the finished product.
For letter envelopes, it is usually necessary to provide two crosswise score lines on the corresponding pre-cut blank, spaced apart from one another at a spacing distance corresponding to the height of the finished letter envelope. These two score lines are typically each produced respectively in a quick impact-stroke manner. Any inaccuracies arising in this context must be manually corrected after shutting off the machine by appropriate corrective adjustments on the scoring blade roller. To achieve this, and to remove any other interferences or defect-producing errors, the scoring blade roller is typically mounted in a tiltable or pivotable manner on the machine frame. In this context it is further typical to provide complicated bridge and frame constructions for supporting the tiltable and usually driven scoring blade roller. After the removal or correction of any such errors or inaccuracies, it is quite time consuming or complicated to again engage the drive wheel of the scoring blade roller in the drive line of the machine in a proper and exactly registered manner in order to restart the operation of the machine. Substantial problems also arise in the unguided output of blanks out of the apparatus, and especially for blanks having lateral points, peaks, or corners.
It has also been especially difficult to properly feed thin flexible blank materials such as paper envelope blanks. Conventional scoring machines feed and advance the material in a flat plane between the scoring roller and the counter roller by pushing the material along a flat table. Such a pushing feed advance is provided by pushing the blank from its trailing edge using pusher dogs, drive chains or the like, or by pinching and pushing the blank in the nip formed between two feed rollers, for example. While such a feed may be adequate for relatively stiff cardboard and the like, it has been found in practice to be unsuitable for flexible materials such as paper. Namely, the flexible blank has a tendency to crumple or shift improperly while it is being pushed, and also has a tendency to curl or deflect out of the intended flat planar feed advance path. Also, regardless of the material, such conventional apparatus and methods suffer problems due to the difficulty of the required synchronization between the flat planar feed advance and the rotational motion of the scoring roller and the counter roller.
In view of the above it is the aim of the invention to provide an improved method and apparatus for forming score lines on pre-cut sheet blanks, and especially envelope blanks, that avoid or overcome the above described difficulties and disadvantages of the prior art, and achieve further advantages that are apparent from the present description.
The above objects have been achieved in a method for forming score lines on a pre-cut sheet blank using a scoring blade roller and a counter roller according to the invention, wherein the blank is pulled by vacuum applied to its leading edge portion in the transport direction at least during the formation of the crosswise score line, and wherein the rear or tail portion of the blank behind the crosswise score line in the transport direction is only loosely guided along and is not held by vacuum or by other means so that this rear or tail portion of the blank is freely movable, i.e. is not rigidly held, to allow it to undergo compensating movements during the formation of the score line. Moreover, the blank is pulled and transported by the scoring blade roller itself. The pulling vacuum is applied via the scoring blade roller, and the blank partially wraps around the scoring blade roller for proper guidance.
Previously, it has been typical for carrying out the score line formation, that the pre-cut blank was clampingly held on both sides of the scoring blade roller and its counter tool, and a pushing force was applied to the blank essentially at a location behind, in the transport direction, the crosswise score line that was to be formed. Contrary thereto, according to the invention, the blank is now held or engaged in the area of its forward edge or forward margin before the formation of the score line, and then the blank is held and guided along this forward edge or margin during the transport of the blank through the scoring station. The rear or tail end of the blank is no longer held and is therefore freely able to carry out any necessary compensating movements or positional adjustments if the material of the blank must yield toward the blank""s forward edge, which continues to be transported exactly in registration, during formation of the crosswise score lines. The inherently disadvantageous material characteristics or properties, for example as are possessed by a rigid and non-elastic paper material, therefore can no longer lead to production difficulties and errors, which makes it possible to increase the piece count output of a production machine as compared to the prior art.
The above mentioned objects have further been achieved in an apparatus for forming crosswise score lines on pre-cut blanks of predominantly non-elastic material, according to the invention, wherein the apparatus includes a machine frame, a drive, at least one scoring blade roller, and a counter roller. Particularly according to the invention, the scoring blade roller comprises a suction shell with a plurality of circumferentially arranged suction openings, which may be connected to a source of vacuum suction.
Preferably the scoring blade roller includes a first scoring blade that is rigidly fixed in position and a second scoring blade that is adjustable to various circumferential positions relative to the first scoring blade. Thereby the second scoring blade may be adjusted to different format sizes of the blanks to be scored, and particularly different spacings between the two score lines to be provided on each blank. Also, the suction for holding the leading edge portion of each blank is provided through the plural suction openings or holes in a suction shell forming a partial circumferential sector-shaped part of the scoring blade roller. The suction shell extends only over a first angular range, e.g. less than 180xc2x0, and does not include any scoring blade within this range. On the other hand, the scoring blades are arranged in a second angular range that does not include any suction holes and that extends over an angle complementing the first angular range to form the complete 360xc2x0 circumference of the scoring blade roller. Preferably there is a single first angular range and a single second angular range that together make up the 360xc2x0 circumference, but there could be two first angular ranges (with respective suction shells) and two second angular ranges (with respective scoring blades) arranged alternately in succession making up the 360xc2x0 circumference. Thereby, for example, two successive blanks may be transported and scored during each rotation of the scoring blade roller. The suction shell may be fixed or adjustable relative to the fixed first scoring blade.
According to further details of the invention, the suction openings or holes are grouped together into respective groups that are respectively controllable or actuatable in a selectively targeted manner. In this context it is particularly advantageous if the suction openings on the circumference of the suction shell are grouped together into respective axis-parallel groups that are respectively connectable in a row-by-row manner to a suction conduit or line, in order to be able to adapt the particular suction configuration to various formats of the blank. Particularly, a single row or a group of e.g. two or three rows of the suction openings can be selected and actuated with suction. The particular row or group of rows selected depends on the format size of the blanks to be scored. Namely, the appropriate row or rows of suction openings will be selected to correspond to the location of the forward leading edge margin of the blank on the scoring roller or particularly on the suction shell, and to establish the proper spacing between the leading edge of the blank and the location at which the fixed first scoring blade is to form the first score line. Thus, a proper selection of which row or rows of the suction openings to be actuated with suction can partially or entirely replace the need for making the suction shell physically circumferentially adjustable with respect to the scoring roller shaft and the fixed first scoring roller. The number of rows selected in a group will, for example, relate to the amount of suction holding power that needs to be applied to the leading edge margin portion of the blank, which in turn depends on the format size of the blank. The single row or group of rows that is selected will be constantly supplied with a suction vacuum as that row or group rotates around the axis of the scoring roller, at least over the rotation angle in which the leading edge portion is to be held by vacuum against the scoring roller.
In order to controllably actuate and deactuate the suction openings, the suction shell comprises a plurality of suction channels extending parallel to the axis of the scoring blade roller. Furthermore, each axis-parallel suction channel is connectable in a freely selectable manner to a main vacuum channel that is arranged extending axially in the drive shaft of the scoring blade roller. In order to achieve this, in addition to a typical suction air control head at one end of the drive shaft, the present apparatus further includes a suction air selector ring arranged preferably in the middle of the scoring blade roller. This suction air selector ring on the one hand has a radial bored hole arranged in the drive shaft and leading to the main vacuum channel, and on the other hand has an internal circumferential groove and a radial bored hole leading to the suction channels in the suction shell. By means of these structural features of the apparatus, the above described method according to the invention may be carried out.